How can I keep my photo sort order when importing to Photos?

If your filenaming is alphabetic, you can put the photos in an album and (or if they are already in an album) right click the album and select sort>keep sorted by title.

That should then sort by filename.

Try this AppleScript first, Script: Changing the Title to the Filename without Extension, on the photos is the album and then do a Sort by Title. Also there must not be any text in the Title field for the script to work.

The script compiled as an application can be downloaded from this tutorial site:  P01 - Applescripts from Photos’ User Tips Compiled as Applications.  To launch it the first time Control (right) - click on it and select Open from the contextual menu. 

The first time you launch the app Control (right) - click on it and select Open from the contextual menu.

So renamed in finder?

No doubt - I meant previously imported into your library, not someone else's.

So you use file>import to bring them into photos.

It is not possible for photos to know the previous filename - unless you've previously imported them and not fully deleted them from the library. The filename is not stored anywhere except in the filename, if you've changed that, then the original one is not stored anywhere. There is nowhere for photos to get it from.

Try creating a new empty library, and importing them into that. (Hold down the option key while starting photos, and click "create new"

Hi

How and where are you changing the filenames?

Are these files that have been previously imported?

How are you importing them after the change?

What do you see under the thumbnail in the album view with view>metadata>titles enabled? If it is not the filename you are expecting, have you also set titles for these images in the info pane?